This invention relates to a rotary commutator valve that is located at the exhaust ports of the cylinder of an engine for regulating the flow of exhaust and allowing the exhaust ports to be sequentially utilized as supplementary intake ports for charging the engine cylinder. The rotary commutator valve of this invention can be incorporated into the high-pressure, high-efficiency engines disclosed in our U.S. Pat. No. 4,809,646, issued Mar. 7, 1989, entitled HIGH PRESSURE RECIPROCATOR, U.S. Pat. No. 4,791,787, issued Dec. 20, 1988, entitled REGENERATIVE THERMAL ENGINE U.S. Pat. No. 4,841,928, issued June 27, 1989, entitled RECIPROCAL ENGINE WITH FLOATING LINER and in our U.S. patent application Ser. No. 341,533, filed Apr. 21, 1989, entitled OPTIMIZED HIGH PRESSURE COMBUSTION ENGINES. In a high-pressure, high r.p.m. engine, the period of time within which to exhaust the combustion gases and charge the cylinder with air, particularly in a two-cycle engine, is extremely brief. Where high peak compression is to be obtained, the effective entry area of the ports for incoming air should equal or exceed the cross sectional area of the cylinder. In this manner the air does not have to expand and after passing through the ports, a maximum charge of air can be obtained by the inertial effect of incoming air when the port opening and closure is properly timed.
Furthermore, in a high-pressure, short-stroke engine, where ports are located in the circumferential wall of the cylinder for intake or exhaust of air when the ports are exposed as the piston reaches the bottom dead center of its cycle, minimizing the height of the ports is of extreme importance to maximize the effective stroke of the piston and hence the compression ratio. Since the compression does not effectively begin until the ports are sealed by the passing piston, the lower the profile of the ports, the greater will be the ultimate compression.
In conventional two-cycle engines where both intake and exhaust ports are located in the wall of the cylinder, the exhaust ports customarily have a higher profile than the intake ports to allow the exhaust gases at high pressure to begin to exhaust through the exhaust ports before the intake ports are exposed and incoming air is admitted to scavenge and charge the cylinder. Because the exhaust ports remain open while the intake ports are exposed, the cylinder is frequently over scavenged wasting precompressed air. Although the rotary commutator valve of this invention is primarily designed for use in two-cycle engines, it can also be applied to four cycle systems, and systems that incorporate a combination of cylinder wall ports and poppet valves.
In general, throughout this application the use of the term ports will be used to indicate the inlet and exhaust openings to the cylinder even though in some cases the openings may actually be regulated by such poppet valves. In an attempt to control the over scavenging of the cylinder, and prevent loss of excessive air, the cylinder is usually incompletely scavenged and a portion of the exhaust gases will remain in the cylinder for subsequent compression with the new charge of air. The scavenging efficiency is usually determined according to the proportion of residual gases to the fresh charge and is usually between 60 and 75% in existing engines. Where the intake air is carbureted, overscavenging can result in the loss of unburned fuel. In addition to the deleterious effect on fuel efficiency, unburned hydrocarbons contribute to environmental pollution and are unacceptable in a modern engine system. The failure to adequately control the entry of air and exhaust of combustion gases has limited the application of two-cycle engines for general automotive use. These problems have been resolved by the rotary commutator valve described herein.
Furthermore, the rotary valve system can be applied to four-cycle engines to improve performance and provide for efficient charging of the engine by permitting the exhaust port to supplement as an intake port after the exhaust phase has been completed. The rotary commutator valve has particular application in a two-cycle, opposed-piston engine that is designed for high pressure operation as described herein.